The long range goal of this proposal is the elucidation of the mechanisms whereby embryonic cells are directed into particular developmental pathways. In Drosophila, the developmental fate of different regions of the blastoderm is thought to depend on the special organization of the egg cytoplasm. The work outlined here represents a genetic analysis of this phenomenon and will use mutations to characterize the positional information in the egg, to study how it arises during oogenesis and how it is registered in the individual cells and controls their fates. One part of the proposal involves large scale mutagensis experiments aimed at the identification of all maternal effect loci which produce changes in the visible morphology of the eggs or te embryonic development which occurs in them. Once such mutations are obtained, their phenotypes will be studied to determine the extent to which embryonic distinctions such as anterior-posterior polarity, dorsal-ventral polarity and germline-soma are interrelated and can be affected by the same maternally active genes. Mutations altering chorion pattern will be studied to determine the relationship between the events during oogenesis which control the pattern of the egg coverings and those effecting the spacial organization of embryonic determinants. Germline mosaics will be constructed using pole cell transplantation and mitotic recombination to determine whether each mutation affects germ-line or somatic cells. An attempt will be made to induce mosaicism within the oocyte nurse cell complex. To gain insight into the early response of the blastoderm nuclei to the positional information of the egg, saturation mutagensis experiments will also be carried out to identify X-linked loci required in the zygotic genome for normal embryonic pattern. These will be compared to the lethal loci already obtained in saturation screens for autosomal loci. Living mutant embryos will be examined to determine the earliest deviations from normal development. Larval gynandromorphs will be constructed to determine whether the wild type gene products are required only in particular regions of the embryo and whether the expression of mutant phenotypes is autonomous in small patches of mutant cells.